1. Field of the Invention
The present invention relates to an electrode layer for thin-film magnetic heads.
2. Description of the Related Art
Thin-film magnetic heads include electrode layers for applying currents to magnetoresistive sensors and detect magnetic fields leaking from recording medium using a magnetic resistance effect when currents are applied to the magnetoresistive sensors via the electrode layers. In the thin-film magnetic heads, in order to minimize the electrical resistances of components other than the magnetoresistive sensors, the electrode layers preferably contain a metal material, such as Au, having a small resistivity. In general, a known electrode layer containing Au includes a Ta base sub-layer for preventing Au from diffusing, an Au sub-layer functioning as a main conductive layer, and a Ta protective sub-layer for preventing smear from occurring, those sub-layers being disposed in that order.
In the Ta/Au/Ta multilayer structure, since the Au sub-layer is inferior in electromigration (EM) resistance, Au atoms are ejected from the Au sub-layer because electrons moving in the electrode layer collide with the Au atoms. Therefore, there is a problem in that cavities are formed in the electrode layer while a current is applied to the electrode layer over a long period time, that is, a thin-film magnetic head is used over a long period time. The cavities formed in the electrode layer causes an increase in the electrical resistance of the electrode layer, although the electrode layer contains Au with low resistivity.
In order to improve the EM resistance, some electrode layers have a Ta/Cr/Au/Cr/Ta multilayer structure in which Cr sub-layers are each placed between the Au sub-layer and the corresponding Ta sub-layers. However, in the electrode layers having such a structure in which the Au sub-layer is adjacent to each Ta sub-layer, there is a problem in that heat treatment such as resist-curing or annealing causes an increase in the electrical resistance.
The above electrode layers are disclosed in the patent documents described below.                Japanese Unexamined Patent Application Publication No. 2002-25013        Japanese Unexamined Patent Application Publication No. 2002-208744        Japanese Unexamined Patent Application Publication No. 2002-299725        Japanese Unexamined Patent Application Publication No. 2002-319722        U.S. Pat. No. 6,430,012 B1        